switch a bunch of places to mnt_want_write_file()

it's both faster (in case when file has been opened for write) and cleaner.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index ed083b9..a9aa2f1 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -147,7 +147,7 @@
 	status = -EEXIST;
 	if (dentry->d_inode)
 		goto out_put;
-	status = mnt_want_write(rec_file->f_path.mnt);
+	status = mnt_want_write_file(rec_file);
 	if (status)
 		goto out_put;
 	status = vfs_mkdir(dir->d_inode, dentry, S_IRWXU);
@@ -268,7 +268,7 @@
 	if (!rec_file || !clp->cl_firststate)
 		return;
 
-	status = mnt_want_write(rec_file->f_path.mnt);
+	status = mnt_want_write_file(rec_file);
 	if (status)
 		goto out;
 	clp->cl_firststate = 0;
@@ -311,7 +311,7 @@
 
 	if (!rec_file)
 		return;
-	status = mnt_want_write(rec_file->f_path.mnt);
+	status = mnt_want_write_file(rec_file);
 	if (status)
 		goto out;
 	status = nfsd4_list_rec_dir(purge_old);